1. Field of the Invention
The invention relates to a method and system for detecting errors in a digital data stream being received by a modem after it has been sent by one or more modems over communication channels such as telephone lines.
2. Description of the Prior Art
Digital modems require a means to detect when errors are likely to be occurring in the digital data stream being received. Error detectors currently in use typically flash a warning light when conditions are marginal or to indicate that the modem needs to retrain due to a loss of synchronization with the modem(s) at the other end of the communications link. A crucial need of many modems presently in use is the need to determine the data error rate so that the modem can adapt its maximum data rate to particular transmission channel conditions.
Modems presently in use error signals derived from the demodulation function. These error signals are derived by subtracting a received demodulation symbol from an ideal reference symbol. The error signals are averaged over a period of time and the average value is compared to a reference threshold. Since averaging is involved, this method may not accurately predict data errors in the presence of short term transients such as impulse hits.